1. Field of the Invention
This invention provides a process for preparing water-soluble hydrophobe-containing polymers by a modified inverse polymerization technique. These polymers which will generally also contain cationic functionality to increase their use in oily water clean-up, contain both water soluble monomers and water insoluble monomers. Preferably, the water soluble monomers are acrylamide (AM) and a salt of an unsaturated amine base (C) and the water insoluble monomer is a higher alkyl(meth)acrylamide or alkyl(meth)acrylate (R). These polymers will hereafter be referred to as C-RAM. The process for their preparation relies on placing the water insoluble hydrophobic monomer in the aqueous phase of an inverse, i.e. water-in-oil, emulsion and conducting the entire polymerization in that aqueous phase. Redox, azo, peroxide or other water soluble free radical initiators are used to copolymerize both the water soluble and hydrophobic monomers, forming copolymers of ethylenically unsaturated amine base salts, alkyl(meth)acrylamides or alkyl(meth)acrylates, and acrylamide. These polymers provide exceptional clean-up of waste waters containing organic contaminants. Also they are very effective for resolving oil-in-water emulsions, such as those found in oil production.
2. Description of the Prior Art
The production of waste water clean enough for safe disposal continues to be a problem, especially when oil is emulsified in the primary waste water. In oil production, especially where high levels of water flooding or steam flooding are being practiced, oil-in-water emulsions are generated. Other oil-in-water emulsions of concern in the waste water treating area are those produced as a result of steel mill and metal working operations, food processing, refinery and chemical plant operation, cooling water blow-down, bitumen extraction from tar sands and shale oil operations, rain water run-off and a host of others. These emulsions all have in common the fact that the oil or organic phase is insoluble in the water continuous phase. The amount of oil dispersed in these water continuous emulsions varies from a few to several hundred parts per million, in waste waters, to several percent (5 to 25% or more) in fluids right out of the wellhead.
The oil is generally well dispersed in the water phase as very small droplets that are stabilized as a result of the presence of natural surfactants. The stability of these oil-in-water emulsions generally results from either a negative charge imparted to the droplets by these surfactants, or from steric stabilization caused by surfactants, or by shear which the fluid experiences during production, which causes the generation of smaller and more stable droplets, or from several other sources.
Various chemicals, surfactants and polymers are generally applied to these waters to enhance the separation of oil and water. These chemicals are used to aid in foam generation in flotation. In addition they may be used to cause oil droplet surface charge neutralization, which results in destabilization of the oil-in-water emulsion. The destabilization results in agglomeration of the oil droplets, floc formation and, possibly, several other beneficial effects. While the use of such chemicals generally enhances the separation of oil from oil-in-water emulsions, there remains significant room for improvement. The type of water soluble polymers currently used are generally acrylamide copolymers or melamine/formaldehyde polymers or others. For example, Bolhofner, in U.S. Pat. No. 4,472,284, describes the treatment of water containing fats, oils and greases using a melamine-formaldehyde condensation product, alone or in combination with a polyacrylamide. Rather high polymer concentrations are needed and a two polymer system can present handling difficulties during field operations.
Another approah to the treatment of waste water involves the use of water insoluble polymeric adsorbents, as described by Renner in U.S. Pat. No. 3,716,483, or Takegani et al. in U.S. Pat. No. 4,081,403. These processes for treating waste water are costly and cannot achieve the degree of clean-up of the polymers produced by the process of the present invention.
Another approach involves the use of copolymers of acrylamide with various cationic monomers of various comonomer ratios. Some of the cationic monomers that have been used are: methacrylamidoalkyltrimethylammonium salts, such as methacrylamidopropyltrimethylammonium chloride (MAPTAC), as described in U.S. Pat. No. 4,160,742, or similar acrylate esters; diallyl dialkyl ammoniumm salts, as described by Booth and Linke in U.S. Pat. Nos. 3,147,218 and 3,316,181; salts of dimethylaminoethylmethacrylate and the like. Buris et al., U.S. Pat. No. 4,224,150, describe a process for clarifying aqueous systems employing quaternary ammonium adducts of polymerizable tertiary ammonium salts and acrylamide. These polymers are generally available as high molecular weight materials, either in aqueous solution, as emulsions of various types, or in solid form, which requires dissolution before use.
The use of hydrophobic groups on water soluble polymers to enhance the rheological properties of water based fluids has been described. One approach to provide polyacrylamide based systems containing hydrophobic groups is described by Bock et al., U.S. Pat. No. 4,520,182. Water soluble acrylamide copolymers containing a small amount of oil soluble or hydrophobic alkyl acrylamide groups were found to impart efficient viscosification to aqueous fluids. Landoll, U.S. Pat. No. 4,304,902, describes copolymers of ethylene oxide with long chain epoxides which also required relatively large polymer concentrations (approximately 1%) for thickening water and required surfactants for solubility due to irregularities in the polymerization. In a related case, U.S. Pat. No. 4,428,277, modified nonionic cellulose ether polymers are described. Although these polymers show enhanced viscosification relative to polymers not containing hydrophobic groups, the viscosification efficiency was very low, requiring 2 to 3 weight percent polymer to provide an enhancement. The use of surfactants to enable solubility and, in turn, viscosification by a water soluble polymer containing hydrophobic groups is described by Evani, U.S. Pat. No. ,4,432,881. The need for a surfactant to achieve solubility and thickening efficiency should make such a system very salt sensitive, as well as very sensitive to small changes in surfactant and polymer concentration. Emmons et al., U.S. Pat. No. 4,395,524, teaches acrylamide copolymers as thickeners for aqueous systems. While these polymers possess hydrophobic groups, they do not contain the cationic monomers disclosed in this invention and are not effective in treating oil-in-water emulsions or viscosifying water-based fluids.
One of the objects of this invention is to overcome the deficiencies in the use of the water soluble polymers of the prior art for treating oily waste water and resolving oil-in-water emulsions. A new class of water soluble polymers, described in copending application U.S. Ser. No. 904,548, filed Sept. 8, 1986 (now abandoned) and continuation U.S. Ser. No. 054,382, filed May 26, 1987 now U.S. Pat. No. 4,835,234, can be used at a lower treat rate and hence is more efficient than prior art materials for oily water treatment. Furthermore, these novel terpolymers provide a superior degree of clean-up or oil removal in comparison to the prior art materials. These new polymers contain a nonionic water soluble monomer, such as acrylamide, a cationically charged, water soluble, ethylenically unsaturated amine-based monomer, such as 3-methacrylamidopropyltrimethylammonium chloride (MAPTAC), and a water insoluble or hydrophobic monomer, such as an alkyl(meth)acrylamide or alkyl(meth)acrylate with a chain length of 4 carbons or greater.
When these polymers are placed in an aqueous solvent, the hydrophobic groups aggregate or associate in a manner similar to a surfactant. If oil droplets are present in an aqueous solution there is an attractive interaction between the hydrophobic groups and the hydrophobic oil droplets. We have found that the presence of cationic groups, such as 3-methacrylamidopropyltrimethylammonium chloride (MAPTAC) causes an expansion of the polymer in solution, an improvement in polymer solubility, and an enhancement of the attractive interaction between the polymer chains and the oil droplets which normally have negative surface charges. The synergism between the cationic and hydrophobic groups in terms of oily water treatment or breaking of oil-in-water emulsions sets these polymers apart from those of the prior art.
Synthesis of polymers containing both hydrophobic and hydrophillic functionality presents difficulties. In order for polymerization to be effected, the monomers must obviously come into close proximity to one another. The incompatibility of the oil soluble and water soluble monomers in water, as the solvent, prevents an effective concentration of one or the other of these monomeric species from being achieved at the locus of polymerization of the other comonomer. Several processes described in the prior art could conceivably achieve this, but have serious deficiencies, necessitating this invention. For example, simply dispersing the water insoluble monomer as fine particles in the aqueous medium containing dissolved water soluble monomers would result in low incorporation of the water insoluble monomer and would lead to a heterogeneous product of particles dispersed in a predominantly water soluble polymer. The resulting polymer could not be used to impart efficient and uniform thickening to water based fluids, nor be very effective in treating oily water.
Techniques for polymerizing water soluble polymers, such as those taught in U.S. Pat. No. 4,154,190, 3,211,708, 3,002,960 and 3,284,393, cannot be used to prepare the compositions of this invention. Also, techniques or processes for preparing cationic polymers or copolymers containing cationic monomers, such as U.S. Pat. Nos. 4,452,957, 4,283,517, 4,160,742 and 3,316,181, have deficiencies in terms of incorporating the hydrophobic monomers needed for the polymers of this invention. This art does not teach the formation of a sufficiently fine dispersion of the water and oil soluble monomers to enable uniform reaction and homogeneous terpolymers to be produced. The use of mutual solvents or solvent mixtures to dissolve the water and oil soluble monomers, as taught by Lenke et al., U.S. Pat. No. 4,098,987, has some serious limitations. Although this approach undoubtedly allows the incompatible monomers to come into close proximity to one another, since the dispersion is on a molecular scale, often the resulting copolymer is insoluble in the same solvent, as shown in U.S. Pat. No. 4,151,333. This leads to precipitation of the copolymer before it has achieved sufficient molecular weight to provide effective oily water treatment. The nonionic polymeric surfactants taught in U.S. Pat. No. 4,098,987 possess extremely low molecular weight (less than 10,000 amu) and lack the cationic functionality necessary for the present polymers. Thus, these teachings provide polymers which do not provide the extent or efficiency of oily water clean-up or breaking of oil-in-water emulsions. A major objective of this invention is to teach a process for preparing water dispersible or water soluble polymers containing both hydrophobic and cationic functionality. A further objective is to provide a process for producing these polymers for treatment of oily water.
Two techniques have been found most useful for preparing hydrophobically associating copolymers of acrylamide and alkylacrylamides. The first method was based on the use of a water continuous microemulsion to disperse the oil soluble monomer in a solution of the water soluble monomers. Details of the procedures and techniques are taught by Turner et al., U.S. Pat. No. 4,521,580. A second method for preparing copolymers of acrylamide and alkylacrylamide was based on dispersing the oil soluble monomer using low HLB surfactants to form an aqueous micellar solution which contains the water soluble monomers. Suitable surfactants and the details of the polymerization are taught by Turner et al., U.S. Pat. No. 4,528,348. While either the microemulsion or micellar polymerization techniques can be used to prepare hydrophobically associating polymers containing a variety of water soluble nonionic monomers, a problem arises when the monomers have a strong interaction with the surfactants used in the polymerization. In particular, strong ionic interactions or complexes can be formed between cationic water soluble monomers, such as ethylenically unsaturated amine based monomers, and anionic surfactants, such as alkyl sulfates and sulfonates.
A third technique which also has been found useful for preparing hydrophobically associating copolymers of acrylamide and alkylacrylamides is based upon a solution polymerization technique. The solution polymerization utilizes mutual solvents, i.e. alcohols or acetone, with water to provide effective copolymerization of water soluble and water insoluble monomers. The resultant polymeric solutions are generally of very low molecular weight due to the large amounts of solvent used since the solvent acts as a chain transfer agent during polymerization. Low molecular weight products are not effective in cleaning up oily water.
All three of the techniques suffer the same low total solids content, typically less than 10 weight percent to be flowable in the reactor.
A process is described in this application which overcomes the described problems. The present invention teaches the use of a modified water-in-oil emulsion polymerization technique to provide effective copolymerization of water soluble and water insoluble monomers. The modified technique entails incorporating the water insoluble monomers into the aqueous phase along with the water soluble monomers and then utilizing a novel surfactant system to maintain the stability of the water-in-oil emulsion during the subsequent polymerization which is conducted solely in the aqueous phase.